1. Field of the Invention
The present invention relates to an image data alteration preventing apparatus, an image data alteration preventing method, a scrambled image producing method, an image reproducing apparatus, and a digital VTR.
2. Description of the Prior Art
[1] A recording apparatus for continuously or intermittently recording an image picked up by a monitoring camera on a video tape by a video tape recorder (VTR) has already been developed.
The contents recorded on the video tape by such a recording apparatus maybe altered. In a case where the contents recorded on the video tape are altered, examination is performed with the truth distorted unless it is recognized that the contents are altered, which may cause social confusion.
An object of the present invention is to provide an alteration preventing apparatus and an alteration preventing method in which it is possible to judge whether or not image data recorded on a recording medium is altered, and prevent the image data from being altered.
[2] A digital VTR for continuously or intermittently recording on a video tape an image picked up by a monitoring camera after coding the image has already been developed.
It is not preferable that the image recorded on the video tape by such a digital VTR is freely reproduced by a person other than a particular person because it is deeply related to privacy.
An object of the present invention is to provide a scrambled image producing method in which a scrambled image can be produced when image coding data obtained by image coding is decoded.
An object of the present invention is to provide an image reproducing apparatus capable of reproducing, when an image is reproduced from a recording medium having image coding data obtained by image coding recorded thereon, a scrambled image.
An object of the present invention is to provide an image reproducing apparatus and a digital VTR which reproduce, when an attempt to reproduce an image is made by a person other than a particular person, a scrambled image.
An image data alteration preventing apparatus according to the present invention is characterized by comprising recording means for producing first alteration detecting data on the basis of image data, to record the produced first alteration detecting data, together with the image data, on a recording medium, and examining means for producing second alteration detecting data on the basis of the image data read out of the recording medium, and collating the produced second alteration detecting data and the first alteration detecting data read out of the recording medium, to judge whether or not the image data read out of the recording medium is altered. The image data may be digital image data or compressed coding data.
An example of the recording means is one comprising means for blocking in field units the image data such that the width thereof is previously determined n bytes long, means for subjecting image data for each block to a predetermined first operation in the longitudinal direction, to obtain first alteration detecting data which is n bytes long, and means for recording the first alteration detecting data, together with the image data, on the recording medium, and an example of the examining means is one comprising means for blocking in field units the image data read out of the recording medium such that the width thereof is previously determined n bytes long, means for subjecting image data for each block to the first operation in the longitudinal direction, to obtain second alteration detecting data which is n bytes long, and means for collating the obtained second alteration detecting data and the first alteration detecting data read out of the recording medium, to judge whether or not the image data read out of the recording medium is altered.
An example of the recording means is one comprising means for blocking in field units the image data such that the width thereof is previously determined n bytes long, means for subjecting image data for each block to a predetermined first operation in the longitudinal direction, to obtain the result of the operation which is n bytes long, means for subjecting the obtained result of the operation to a predetermined second operation, to obtain first alteration detecting data which is n bytes long, and means for recording the first alteration detecting data, together with the image data, on the recording medium, and an example of the examining means is one comprising means for blocking in field units the image data read out of the recording medium such that the width thereof is previously determined n bytes long, means for subjecting image data for each block to the first operation in the longitudinal direction, to obtain the result of the operation which is n bytes long, means for subjecting the obtained result of the operation to the second operation, to obtain second alteration detecting data which is n bytes long, and means for collating the obtained second alteration detecting data and the first alteration detecting data read out of the recording medium, to judge whether or not the image data read out of the recording medium is altered.
An image data alteration preventing method according to the present invention is characterized by comprising the recording step of producing first alteration detecting data on the basis of image data, to record the produced first alteration detecting data, together with the image data, on a recording medium, and the examining step of producing second alteration detecting data on the basis of the image data read out of the recording medium, and collating the produced second alteration detecting data and the first alteration detecting data read out of the recording medium, to judge whether or not the image data read out of the recording medium is altered. The image data may be digital image data or compressed coding data.
An example of the recording step is one comprising the steps of blocking in field units the image data such that the width thereof is previously determined n bytes long, subjecting image data for each block to a predetermined first operation in the longitudinal direction, to obtain the first alteration detecting data which is n bytes long, and recording the first alteration detecting data, together with the image data, on the recording medium, and an example of the examining step comprises the steps of blocking in field units the image data read out of the recording medium such that the width thereof is previously determined n bytes long, subjecting image data for each block to the first operation in the longitudinal direction, to obtain the second alteration detecting data which is n bytes long, and collating the obtained second alteration detecting data and the first alteration detecting data read out of the recording medium, to judge whether or not the image data read out of the recording medium is altered.
An example of the recording step is one comprising the steps of blocking in field units the image data such that the width thereof is previously determined n bytes long, subjecting image data for each block to a predetermined first operation in the longitudinal direction, to obtain the result of the operation which is n bytes long, subjecting the obtained result of the operation to a predetermined second operation, to obtain first alteration detecting data which is n bytes long, and recording the first alteration detecting data, together with the image data, on the recording medium, and an example of the examining step is one comprising the steps of blocking in field units the image data read out of the recording medium such that the width thereof is previously determined n bytes long, subjecting image data for each block to the first operation in the longitudinal direction, to obtain the result of the operation which is n bytes long, subjecting the obtained result of the operation to the second operation, to obtain second alteration detecting data which is n bytes long, and collating the obtained second alteration detecting data and the first alteration detecting data read out of the recording medium, to judge whether or not the image data read out of the recording medium is altered.
A scrambled image producing method according to the present invention is characterized by comprising the step of performing, when image coding data obtained by image coding is decoded, inverse quantization using a quantization table different from a quantization table used at the time of the image coding, to produce a scrambled image.
A first image reproducing apparatus according to the present invention is an image reproducing apparatus for reproducing an image from a recording medium having image coding data obtained by image coding recorded thereon, characterized by comprising means for switching a normal play mode and a scramble play mode, means for performing, when the image coding data is decoded, inverse quantization using the same quantization table as a quantization table used at the time of the image coding, to reproduce a normal image at the time of normal play mode, and means for performing, when the image coding data is decoded, inverse quantization using a quantization table different from the quantization table used at the time of the image coding, to reproduce a scrambled image at the time of the scramble play mode.
A second image reproducing apparatus according to the present invention is an image reproducing apparatus for reproducing an image from a recording medium having image coding data obtained by image coding recorded thereon, characterized by comprising means for causing an operator to enter a password when a reproduction instruction is entered by the operator, mode switching control means for judging whether or not the password entered by the operator coincides with a password previously registered, to set the operation mode to a normal play mode when both coincide with each other, while setting the operation mode to a scramble play mode when both do not coincide with each other, means for performing, when the image coding data is decoded, inverse quantization using the same quantization table as a quantization table used at the time of the image coding, to reproduce a normal image in a case where the normal play mode is set by the mode switching control means, and means for performing, when the image coding data is decoded, inverse quantization using a quantization table different from the quantization table used at the time of the image coding, to reproduce a scrambled image in a case where the scramble play mode is set by the mode switching control means.
A digital VTR according to the present invention is a digital VTR for coding an image obtained from a monitoring camera, and then recording the coded image on a video tape, and decoding image coding data recorded on the video tape to obtain reproduction data, characterized by comprising means for causing an operator to enter a password when a reproduction instruction is entered by the operator, mode switching control means for judging whether or not the password entered by the operator coincides with a password previously registered, to set the operation mode to a normal play mode when both coincide with each other, while setting the operation mode to a scramble play mode when both do not coincide with each other, means for performing, when the image coding data is decoded, inverse quantization using the same quantization table as a quantization table used at the time of the image coding, to reproduce a normal image in a case where the normal play mode is set by the mode switching control means, and means for performing, when the image coding data is decoded, inverse quantization using a quantization table different from the quantization table used at the time of the image coding, to reproduce a scrambled image in a case where the scramble play mode is set by the mode switching control means.